Michelle Williams and Jason Segel had plenty to feel giddy about Wednesday night, as the new couple attended the premiere of his movie The Five-Year Engagement at the Tribeca Film Festival – and snuggled together at the afterparty.

They were affectionate throughout the night. As the movie ended, he gave her a little kiss on the cheek, as she took off and he stayed in New York's Ziegfeld Theater to chat with friends and well-wishers.

They were practically inseparable at the afterparty in the Museum of Modern Art. Segel held Williams's hand and took her around to tables, whispering in her ear. They looked very new and very happy. At one point, he pulled her behind a curtain and she came back out and pointed at him jokingly.

Williams, 31, left before Segel, 32 – she leaned in, kissed his cheek, said something quickly in his ear, rubbed his back and dipped out through the curtain.

Speaking generally, not talking about Williams specifically, Segel, who co-wrote the film about an engaged couple who keep delaying their wedding, told PEOPLE about his own grand plans for getting engaged.

"My plan is to get her to marry me as quickly as possible before she finds out who I really am," he said with a laugh. "I'll do it romantic, but I'll do it like over a three-day weekend. We'll meet on Friday, have our first date on Saturday, engaged on Sunday and married on Monday."

Segel certainly seems closer to making that kind of commitment than he used to be. "I hit my thirties and enough became enough," he said. "I'm ready to enter phase three. I put the puppets into a closet. I'm getting nice furniture."

Segel said his goal in making The Five-Year Engagement was to show how complicated relationships are over the long haul. "A lot of people say 'I do' to a moment, but they don't realize they're saying 'I do' to a lifetime," he said.

Asked if he would relocate for love, like his character does, Segel replied: "I would, absolutely."